From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752445AbeDJLRW (ORCPT ); Tue, 10 Apr 2018 07:17:22 -0400 Received: from mail-wm0-f66.google.com ([74.125.82.66]:32954 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751600AbeDJLRV (ORCPT ); Tue, 10 Apr 2018 07:17:21 -0400 X-Google-Smtp-Source: AIpwx4/N1LbLmn3puFfHe+HDKgQ5IUlye6t6D1NxPDfCco+j9GXiJrqhO3LLTcCJ+d86D/SEssft9A== Date: Tue, 10 Apr 2018 14:16:32 +0300 From: "Kirill A. Shutemov" To: Naoya Horiguchi Cc: Michal Hocko , Zi Yan , "linux-mm@kvack.org" , Andrew Morton , Vlastimil Babka , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] mm: shmem: enable thp migration (Re: [PATCH v1] mm: consider non-anonymous thp as unmovable page) Message-ID: <20180410111632.xtrxmop7p5v2mopj@node.shutemov.name> References: <20180403083451.GG5501@dhcp22.suse.cz> <20180403105411.hknofkbn6rzs26oz@node.shutemov.name> <20180405085927.GC6312@dhcp22.suse.cz> <20180405122838.6a6b35psizem4tcy@node.shutemov.name> <20180405124830.GJ6312@dhcp22.suse.cz> <20180405134045.7axuun6d7ufobzj4@node.shutemov.name> <20180405150547.GN6312@dhcp22.suse.cz> <20180405155551.wchleyaf4rxooj6m@node.shutemov.name> <20180405160317.GP6312@dhcp22.suse.cz> <20180406030706.GA2434@hori1.linux.bs1.fc.nec.co.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180406030706.GA2434@hori1.linux.bs1.fc.nec.co.jp> User-Agent: NeoMutt/20180323 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 06, 2018 at 03:07:11AM +0000, Naoya Horiguchi wrote: > Hi everyone, > > On Thu, Apr 05, 2018 at 06:03:17PM +0200, Michal Hocko wrote: > > On Thu 05-04-18 18:55:51, Kirill A. Shutemov wrote: > > > On Thu, Apr 05, 2018 at 05:05:47PM +0200, Michal Hocko wrote: > > > > On Thu 05-04-18 16:40:45, Kirill A. Shutemov wrote: > > > > > On Thu, Apr 05, 2018 at 02:48:30PM +0200, Michal Hocko wrote: > > > > [...] > > > > > > RIght, I confused the two. What is the proper layer to fix that then? > > > > > > rmap_walk_file? > > > > > > > > > > Maybe something like this? Totally untested. > > > > > > > > This looks way too complex. Why cannot we simply split THP page cache > > > > during migration? > > > > > > This way we unify the codepath for archictures that don't support THP > > > migration and shmem THP. > > > > But why? There shouldn't be really nothing to prevent THP (anon or > > shemem) to be migratable. If we cannot migrate it at once we can always > > split it. So why should we add another thp specific handling all over > > the place? > > If thp migration works fine for shmem, we can keep anon/shmem thp to > be migratable and we don't need any ad-hoc workaround. > So I wrote a patch to enable it. > This patch does not change any shmem specific code, so I think that > it works for file thp (not only shmem,) but I don't test it yet. > > Thanks, > Naoya Horiguchi > ----- > From e31ec037701d1cc76b26226e4b66d8c783d40889 Mon Sep 17 00:00:00 2001 > From: Naoya Horiguchi > Date: Fri, 6 Apr 2018 10:58:35 +0900 > Subject: [PATCH] mm: enable thp migration for shmem thp > > My testing for the latest kernel supporting thp migration showed an > infinite loop in offlining the memory block that is filled with shmem > thps. We can get out of the loop with a signal, but kernel should > return with failure in this case. > > What happens in the loop is that scan_movable_pages() repeats returning > the same pfn without any progress. That's because page migration always > fails for shmem thps. > > In memory offline code, memory blocks containing unmovable pages should > be prevented from being offline targets by has_unmovable_pages() inside > start_isolate_page_range(). So it's possible to change migratability > for non-anonymous thps to avoid the issue, but it introduces more complex > and thp-specific handling in migration code, so it might not good. > > So this patch is suggesting to fix the issue by enabling thp migration > for shmem thp. Both of anon/shmem thp are migratable so we don't need > precheck about the type of thps. > > Fixes: commit 72b39cfc4d75 ("mm, memory_hotplug: do not fail offlining too early") > Signed-off-by: Naoya Horiguchi > Cc: stable@vger.kernel.org # v4.15+ This looks sane to me. Acked-by: Kirill A. Shutemov As, yeah, as you mentioned down the thread it's not a stable material -- Kirill A. Shutemov